Polymer brushes form when macromolecular chains are end-tethered to surfaces at high grafting densities. The swelling and mutual steric repulsion of the polymers cause the chains to stretch and extend into the solvent, producing a molecular coating that can reduce non-specific interactions of the underlying surface with cells and biological macromolecules. However, because these brushes are almost universally constructed from synthetic polymers, they are frequently somewhat heterogeneous and are challenging to modify at specific monomeric positions along the chain.